问题补充:
all the homework assigned by the school, the students have to work at it till midnight.
A. Completing
B. To complete
C. Having completed
D. To have completed
答案:
A. Completing
(答案→)B. To complete
C. Having completed
D. To have completed
解析:B 考察非谓语动词。句义:为了完成学校布置的所有作业,学生们不得不写作业到深夜。根据句义可知此处用动词不定式做目的状语。故B正确。